Photodetection and measurement techniques are used by engineers and physicists to "characterize" optical devices and systems. Characterizing — numerically describing a device's performance — is vital to the design and analysis of fiber optics, laser systems, and opto-electronic circuitry. As more and more of electronics are becoming opto-electronic (because light moves faster then electricity) the art of taking accurate, inexpensive optical measurements has become very important to EEs across the board. This is a practical engineering tutorial on making accurate and effective measurements without spending a fortune — by using equipment commonly available in labs and companies. It considers the full chain of equipment: photodetectors, amplifiers, LED sources, electronic drives, basic optics, interference screens, and data acquisition systems. MathCAD will be used for frequency plots throughout.